There is increased interest in water-based paints over oil-based paints for a variety of reasons, including ease of application as well as benefits to the environment. In recent years, there has been considerable pressure from state and federal agencies to reduce volatile organic compounds ("VOCs") in a number of consumer products, including paints, inks, and cosmetics. Hence, there is a substantial need for water-based rheological control agents.
In response to this need for water-based rheological control agents, some companies have begun to develop organoclays that are compatible with water-based gelling systems. Traditionally, organoclays have been prepared from an ion-exchange reaction between a cationic organic compound, which is usually a quaternary amine, and a smectite-type clay with an ion exchange capacity of at least 50 milliequivalents (meq.) weight (wt.) per 100 grams of clay.
Current water-base smectite-type clay systems typically involve surface modification of clays through reaction of alkoxylated quaternary ammonium salts at ion exchange sites to prepare thixotropic agents (as described in U.S. Pat. Nos. 5,663,111; 5,728,764; and 4,677,158) instead of adding traditional quaternary amines such as dimethyl di-hydrogenated tallow amine, and dimethyl hydrogenated tallow benzyl amine. In addition, these processes involve steps for purification and various ion exchange reactions carried out separately and sequentially at elevated temperatures, which adds considerable cost and complexity to the production of organoclays.
In conventional approaches, the steps involved in the process are carried out separately and sequentially, beginning with physical beneficiation of the clay, followed by conversion to a sodium form, and finally, preparation of the organoclay. Normally, the clay in the purified sodium form is separated from a process liquor, dried, and then crushed. The dried, pulverized clay is then repulped in an aqueous medium in preparation for conversion to the organoclay. Multiple drying steps in conventional processes add significantly to the cost of producing organoclays.
Current processes for preparing organoclays are expensive and involve a high content of VOCs used in the process. Furthermore, current approaches subject the clay slurry to high shear in order to disperse the clay and thereby reduce the average particle size of the clay. Combinations of multiple centrifugation steps with multiple, high-energy fluid shear steps are described in the literature. These processes are highly energy intensive and lead to rapid abrasion of processing equipment. An example from U.S. Pat. No. 5,110,501, which illustrates the particle size reduction achieved through high-speed fluid shear, involves the reduction in average particle size from 0.756 micrometers to 0.352 micrometers for a smectite clay with an energy input of 700 HP-hr/ton clay.
In addition, current methods of preparing organoclays that are compatible with water-based systems still rely on the attachment of a water-soluble onium cation onto the clay surface through an ion exchange reaction. This reliance on ion exchange means that the surface coverage of the clay by the organic modifying agent is limited by the number of ion exchange sites per unit area on the clay. Furthermore, once all of the ion exchange sites are occupied through attachment of an organic modifying agent, no further surface modification is possible.
It is therefore an object of the present invention to provide a novel method and apparatus for preparing organoclays for aqueous systems.
It is another object of this invention to provide a novel method for preparing organoclays that can be used to control the rheology of aqueous-based systems.
It is another object of this invention to provide a novel method for preparing organoclays for polar organic systems.
It is another object of this invention to provide a novel method for preparing organoclays for incorporation into polymeric systems as a nanocomposite.
It is another object of this invention to provide a novel method for treating low-grade clay ores to achieve high levels of purification.
It is another object of this invention to provide a novel method for incorporating surface modifying agents onto clay by adsorption through ion-dipole and hydrogen-bonding interactions rather than primary dependence on cation exchange.
It is another object of this invention to provide a novel method for producing highly dispersed organoclays without excessive grinding or high shear dispersion.
It is another object of this invention to provide a novel method for preparing consumer products using a reduced content of VOCs.
It is another object of this invention to provide a novel method for preparing organoclays at a reduced cost compared to current processes.
It is another object of this invention to provide a novel apparatus for preparing organoclays whereby the processing equipment has a prolonged life.
It is another object of this invention to provide a novel method for preparing organoclays having an average particle size of less than 0.2 micrometers using gentle stirring with a mechanical mixer at room temperature.
It is another object of this invention to provide a novel method for preparing organoclays using nonionic polymers for surface modification instead of reliance on ion exchange reactions.
It is another object of this invention to provide a novel method for preparing organoclays for use in foods, pharmaceuticals, cosmetics, and fire retardants.
It is another object of this invention to provide organoclays prepared by a novel method.
It is another object of this invention to provide aqueous compositions containing organoclays prepared by a novel method.
Other objects and advantages of the invention will become apparent by review of the detailed description of preferred embodiments.